P9 - Motion (Year 9)

Question 1

what is the equation for calculating speed?

Answer 1

speed = distance / time

m/s = m / s

Question 2

what equation is used to calculate acceleration?

a = …

Answer 2

a = (v - u) / t

acceleration = (final velocity - initial velocity) / time

(m/s)2 = m/s / s

Question 3

how is constant speed calculated?

Speed & Distance-Time Graphs

Answer 3

∆ distance / ∆ time
–>
∆y / ∆x
–>
(basically find the gradient of the straight line)

Question 4

what does the gradient of a distance-time graph tell you?

Speed & Distance-Time Graphs

Answer 4

the speed

Question 5

rearrange the equation for speed to calculate distance

Speed & Distance-Time Graphs

Answer 5

speed = distance / time
–>
distance = speed x time

(distance would be at the top of the triangle)

Question 6

rearrange the equation for speed to calculate time

Speed & Distance-Time Graphs

Answer 6

speed = distance / time
–>
time = distance / speed

(distance would be at the top of the triangle)

Question 7

speed = ? and velocity = ?

what is the difference between speed and velocity?

Velocity & Acceleration

Answer 7

speed = scalar
velocity = vector*
Speed is just how fast you’re going (e.g. 30mph or 20m/s) with no regard to the direction.
Velocity is speed in a given direction. e.g. 30 mph or 20 m/s, 060°.

(RG p60)

*(the orange dude from despicable me who talks about dircetion and magnitude)

Question 8

how do we calculate acceleration?

Answer 8

1. a = Δv / t
2. acceleration = Δ velocity / time
3. acceleration = (final velocity - initial velocity) / time

Question 9

what is the difference between acceleration and deceleration?

Answer 9

acceleration: speed (or velocity) is increasing
deceleration: speed (or velocity) is decreasing
note: deceleration of 5m/s squared = acceleration of -5m/s squared

Question 10

what does a horizontal line on a velocity-time graph tell you?

Answer 10

no acceleration; constant speed (or velocity)

Question 11

(sketch a velocity-time graph of an object decelerating)

Answer 11

n/a

Question 12

what does the area under a velocity-time graph tell you?

Answer 12

the distance

Question 13

how do we calculate acceleration from a velocity-time graph?

‘for constant…’ and ‘for increasing (or decreasing I guess)…’

Answer 13

constant acceleration:
∆ velocity / ∆ time
–>
∆y / ∆x
–>
(basically find the gradient of the straight line)

increasing acceleration (or decreasing deceleration I guess):
1. draw a tangent for whatever point you need to find the acceleration for; it has to be parallel to the curve at that point
2. draw a triangle (with the tangent line as the hypotenuse)
3. ∆ velocity / ∆ time –> find the gradient of the tangent.

Question 14

how do we calculate distance from a velocity-time graph?

Answer 14

calculate the area under the line

Question 15

how do we calculate speed from a distance-time graph where the object is accelerating?

Answer 15

1. draw a tangent for whatever point you need to find the speed for; it has to be parallel to the curve at that point
2. draw a triangle (with the tangent line as the hypotenuse)
3. ∆ distance / ∆ time
   –>
   ∆y / ∆x
   –>
   (basically find the gradient of the straight line)

Question 16

how do we convert from km/h to m/s?

Answer 16

x1000, /3600

Question 17

how do we convert from m/s to km/h?

Answer 17

x3600, /1000